The objective of the proposed study is to characterize the reactants present in soluble immune complexes in the synovial fluid of patients with rheumatoid arthritis. We propose to: a) dissociate complexes in synovial fluid employing micropreparative electrophoresis, b) characterize the DNA present in these complexes with respect to buoyant density in cesium chloride and melting temperature, c) study the ability of cesium chloride isolated DNA fractions of unique buoyant density to induce synovitis. Synovial fluid will be obtained during periods of active synovitis and the DNA isolated, Millipore filtered and injected intraarticularly at a time when the patient is free of synovitis. Only isologous DNA will be injected and, d) evaluate the role of rheumatoid factor in modifying complement fixation by performing antibody-DNA recombination separately and in the presence of purified 19S IgM rheumatoid factor.